The present invention. relates generally to force-sensing transducers, accelerometers, rate sensors, methods of forming force-sensing transducers, and to methods of forming vibrating-beam force transducers.
Force-sensing transducers can be used to measure force, acceleration, pressure, and the like. One type of force-sensing transducer is a resonating force transducer. Exemplary transducers are described in U.S. Pat. Nos. 5,367,217, 5,339,698, and 5,331,242, the disclosures of which are incorporated by reference. Another type of force-sensing transducer is an accelerometer. Exemplary accelerometers are described in U.S. Pat. Nos. 5,594,170, 5,501,103, 5,379,639, 5,377,545, 5,456,111, 5,456,110, and 5,005,413, which are incorporated by reference herein. Other types of force-sensing transducers can be used as rate sensors. Exemplary rate sensors are described in U.S. Pat. Nos. 5,717,140, 5,376,217, 5,696,323, 5,691,472, and 5,668,329, which are hereby incorporated by reference. Yet other force-sensing transducers can be used as acceleration and rate sensors. Exemplary sensors are described in U.S. Pat. Nos. 5,627,314, 5,557,046, 5,341,682, 5,331,853, 5,331,854, and 5,319,976, the disclosures of which are incorporated by reference herein.
Force-sensing transducers such as those incorporated by reference above, can experience problems associated with metalization which can adversely affect the transducer""s performance. In particular, bias performance can be adversely affected when a conductor having a thermal coefficient of expansion different from that of the substrate, is deposited and used during operation. Specifically, metal conductors can be deposited at high temperatures and, because of the difference in thermal coefficient of expansion with the substrate, the deposited metal conductor can xe2x80x9ccreepxe2x80x9d because of high thermal stress developed between the metal conductor and the substrate. Metal creep occurs when the deposited metal yields during the application of some external stimulant and does not return to its initial condition. The change in condition results in a change in bias operating point.
A preferred conductor material is gold. Gold is typically used in forming metal conductors on such substrates because it exhibits high conductivity and other traits normally associated with noble metals. However, forming the metal conductors using gold exacerbates the adverse effects on bias performance because gold has a very high thermal expansion coefficient relative to typical substrate materials such as quartz and silicon. Additionally, gold has a very low yield strength.
Traditional methods of reducing metal creep include using metal alloys with higher yield strength than pure gold, using alloys with thermal coefficients of expansion closely matched to the particular substrate material, removing metalization layers all together, compensating the metal creep effects by matching metal conductors on opposing surfaces, and designing a very low spring rate support structure to counter the effects of creep.
This invention arose out of concerns associated with providing improved force-sensing transducers, accelerometers, and rate sensors. This invention also arose out of concerns associated with providing improved methods of forming force-sensing transducers such as those mentioned above.
Force-sensing transducers, accelerometers, rate sensors, and methods of forming force-sensing transducers are described.
In one embodiment, a substrate includes a force-sensing element. An adhesion layer is disposed over less than an entirety of the force-sensing element, and a conductive layer is disposed over the force-sensing element and supported in a bonded relationship therewith through the adhesion layer.
In another embodiment, a substrate includes a proof mass and a vibratable assembly connected therewith and configured to detect an acceleration force. An adhesion layer is disposed over less than an entirety of the vibratable assembly, and a conductive path is disposed over the vibratable assembly and fixedly bonded therewith through the adhesion layer.
In another embodiment, a Coriolis rate sensor includes a substrate having a vibratable assembly connected therewith. An adhesion layer is disposed over less than an entirety of the vibratable assembly and a conductive path is disposed over the vibratable assembly and fixedly bonded therewith through the adhesion layer.
In yet another embodiment, a substrate is provided having a force-sensing element defining an area over and within which a conductive layer of material is to be formed. A patterned adhesion layer is formed over less than an entirety of the area. A conductive layer is formed over the area and bonded to the substrate through the patterned adhesion layer.
In still another embodiment, a substrate is provided and etched sufficiently to form a plurality of vibratable beams arranged in a force-sensing configuration. An insulative layer of material is formed over the vibratable beams and an adhesion layer pattern is formed over the vibratable beams. The pattern comprises a plurality of spaced-apart pattern components, with each beam having three pattern components spaced apart along its length. Conductive material is formed over the vibratable beams and the adhesion layer pattern. The conductive material is more fixedly attached to the adhesion layer pattern than to vibratable beam portions not having the adhesion layer pattern thereover. The substrate is temperature cycled effective to weaken the attachment between the conductive material and the vibratable beam portions not having the adhesion layer pattern thereover.